1. Field of the Invention
The present invention relates to a signal processing apparatus, a signal processing method, and a signal processing program that are capable of optimizing an eye opening in an eye diagram of a predetermined signal with high precision.
2. Description of Related Art
In the case of high-speed serial signal transmission, for example, frequency attenuation characteristics of a transmitter or a transmission path may cause a reduction in the area of an eye opening in an eye diagram on a receiver side. For this reason, the receiver is configured to be able to receive data using a function (equalizer function) of widening the eye opening, which is narrowed due to the attenuation characteristics, by using a peaking amplifier or the like. The amount of attenuation varies depending on the characteristics of the transmitter and transmission environments (such as characteristics of a cable). Thus, it is necessary to employ, for example, an adaptive equalizer circuit that detects the amount of attenuation of a transmission path and automatically adjusts the peaking characteristics of an equalizer according to the detected amount of attenuation.
Meanwhile, there is known an adaptive equalizer circuit that detects horizontal jitter characteristics of an eye opening on a receiver side by using a multiphase clock system, to thereby detect the amount of attenuation of a transmission path (e.g., see F. Gerfers et al., “A 0.2-2 Gb/s 6× OSR Receiver Using a Digitally Self-Adaptive Equalizer”, IEEE Journal of Solid-State Circuits, Vol. 43, NO. 6, June 2008). In the adaptive equalizer circuit, a sampler circuit samples an input signal using a six-phase clock system, and performs an exclusive-OR operation on adjacent items of sampled data. Further, in the adaptive equalizer circuit, a counter circuit counts the number of values “1” obtained by the exclusive-OR operation, and a control circuit sums up the numbers of values “1” counted by the counter circuit. Thus, the horizontal jitter characteristics can be detected.
For example, when the eye opening is closed as shown in FIG. 13A, the edge width is large in the count results of the numbers “1” as shown in FIG. 13B. Meanwhile, when the eye opening is opened as shown in FIG. 14A, the edge width is small in the count results of the numbers “1” as shown in FIG. 14B. In this manner, the adaptive equalizer circuit detects the edge width for each amplification level of the equalizer, selects an amplification level of the equalizer at which the edge width is smallest, and fixes the selected amplification level.